Transcript Synovial Joints

9
• Joints
Joints
• Rigid elements of the skeleton meet at
joints or articulations
• Greek root “arthro” means joint
• Articulations can be:
– Bone to bone
– Bone to cartilage
– Teeth in bony sockets
• Structure of joints
– Enables resistance to crushing, tearing, and
Classifications of Joints
• Joints can be classified by function or
structure
• Functional classification – based on
amount of movement
– Synarthroses – immovable – common in
axial skeleton
– Amphiarthroses – slightly movable –
common in axial skeleton
– Diarthroses – freely movable – common in
Classifications of Joints
• Structural classification based on:
– Material that binds bones together
– Presence or absence of a joint cavity
– Structural classifications include
• Fibrous
• Cartilaginous
• Synovial
Fibrous Joints
• Bones are connected by fibrous
connective tissue
• Do not have a joint cavity
• Most are immovable or slightly movable
• Types – sutures, syndesmoses, and
gomphoses
Sutures
• Bones are tightly bound by a minimal
amount of fibrous tissue
• Only occur between the bones of the
skull
• Allow bone growth so that the skull can
expand with brain during childhood
• Fibrous tissue ossifies in middle age
– Synostoses – closed sutures
Syndesmoses
• Bones are connected exclusively by
ligaments
• Amount of movement depends on
length of fibers
– Tibiofibular joint – an immovable
synarthrosis
– Interosseous membrane between radius
and ulna – freely movable diarthrosis
Fibrous Joints
Gomphoses
• Tooth in a socket
• Connecting ligament – the periodontal
ligament
Cartilaginous Joints
• Bones are united by cartilage
• Lack a joint cavity
• Two types – synchondroses and
symphyses
Synchondroses
• Hyaline cartilage unites bones
– Epiphyseal plates
Synchondroses
– Joint between first rib and manubrium
Symphyses
• Fibrocartilage unites bones – resists
tension and compression
• Slightly movable joints that provide
strength with flexibility
– Intervertebral discs
– Pubic symphysis
Symphyses
• Hyaline cartilage – also present as
articular cartilage
Synovial Joints
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•
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Most movable type of joint
All are diarthroses
Each contains a fluid-filled joint cavity
Most are “simple” and have just two
articulating surfaces
• Some are “compound” with more than
two articulating surfaces
– Examples include the elbow and knee
joints
General Structure of
Synovial Joints
• Articular cartilage
– Ends of opposing bones are covered with
hyaline cartilage
– Absorbs compression
• Joint cavity (synovial cavity)
– Unique to synovial joints
– Cavity is a potential space that holds a
small amount of fluid
General Structure of
Synovial Joints
• Articular capsule – joint cavity is
enclosed in a two-layered capsule
– Fibrous capsule – dense irregular
connective tissue – strengthens joint
– Synovial membrane – loose connective
tissue
• Lines joint capsule and covers internal joint
surfaces
• Functions to make synovial fluid
General Structure of
Synovial Joints
• Synovial fluid
– A viscous fluid similar to raw egg white
• A filtrate of blood
– Arises from capillaries in synovial membrane
• Contains glycoprotein molecules secreted by
fibroblasts
General Structure of
Synovial Joints
• Reinforcing ligaments
– Often are thickened parts of the fibrous
capsule
– Sometimes are extracapsular ligaments –
located outside the capsule
– Sometimes are intracapsular ligaments –
located internal to the capsule
A Typical Synovial Joint
General Structure of
Synovial Joints
• Richly supplied with sensory nerves
– Detect pain
– Most monitor how much the capsule is
being stretched
General Structure of
Synovial Joints
• Have a rich blood supply
– Most supply the synovial membrane
– Extensive capillary beds produce basis of
synovial fluid
– Branches of several major nerves and blood
vessels
Synovial Joints with
Articular Discs
• Some synovial joints contain an
articular disc
– Occur in the temporomandibular joint and
at the knee joint
– Occur in joints whose articulating bones
have somewhat different shapes
How Synovial Joints
Function
• Synovial joints – lubricating devices
• Friction could overheat and destroy
joint tissue
• Are subjected to compressive forces
• Fluid is squeezed out as opposing cartilages
touch
• Cartilages ride on the slippery film
Bursae and Tendon
Sheaths
• Bursae and tendon sheaths are not
synovial joints
– Closed bags of lubricant
– Reduce friction between body elements
• Bursa – a flattened fibrous sac lined by
a synovial membrane
• Tendon sheath – an elongated bursa
that wraps around a tendon
Bursae and Tendon
Sheaths
Factors Influencing Joint
Stabililty
• Articular surfaces – seldom play a
major role in joint stability
– The elbow, the knee and the hip do provide
stability
• Ligaments – the more ligaments in a
joint, the stronger it is
• Muscle tone – the most important
factor in joint stability
– Keeps tension on muscle tendons
Movements Allowed by
Synovial Joints
• Three basic types of movement
– Gliding – one bone across the surface of
another
– Angular movement – movements change
the angle between bones
– Rotation – movement around a bone's long
axis
Gliding Joints
• Flat surfaces of two bones slip across
each other
• Gliding occurs
between
– Carpals
– Articular
processes
of vertebrae
– Tarsals
Angular Movements
• Increase or decrease angle between
bones
• Movements involve:
– Flexion and
extension
– Abduction and
adduction
– Circumduction
Angular Movements
Angular Movements
Angular Movements
Rotation
• Involves turning movement of a bone
around its long axis
• The only movement allowed between
atlas and axis vertebrae
• Occurs at the hip and shoulder joints
Special Movements
• Supination – forearm rotates laterally –
palm faces anteriorly
• Pronation – forearm rotates medially –
palm faces posteriorly
Special Movements
• Dorsiflexion – lifting the foot so its
superior surface approaches the shin
• Plantar flexion – depressing the foot –
pointing the toes
Special Movements
• Inversion – turning the sole medially
• Eversion – turning the sole laterally
Special Movements
• Protraction – nonangular movement of
jutting out the jaw
• Retraction – opposite movement to
protraction
Special Movements
• Elevation – lifting a body superiorly
• Depression – moving the elevated part
inferiorly
Special Movements
• Opposition – movement of the thumb to
touch the tips of other fingers
Synovial Joints Classified
by Shape
• Plane joint
– Articular surfaces are flat planes
– Short gliding movements are allowed
• Intertarsal and intercarpal joints
• Movements are nonaxial
• Gliding does not involve rotation around any
axis
Plane Joint
Synovial Joints Classified
by Shape
• Hinge joints
– Cylindrical end of one bone fits into a
trough on another bone
– Angular movement is allowed in one plane
– Elbow, ankle, and joints between phalanges
– Movement is uniaxial – allows movement
around one axis only
Hinge Joint
Synovial Joints Classified
by Shape
• Pivot joints
– Classified as uniaxial – rotating bone only
turns around its long axis
– Examples
• Proximal radioulnar joint
• Joint between atlas and axis
Pivot Joint
Synovial Joints Classified
by Shape
• Condyloid joints
– Allow moving bone to travel:
• Side to side – abduction-adduction
• Back and forth – flexion-extension
• Classified as biaxial – movement
occurs around two axes
Condyloid Joint
Synovial Joints Classified
by Shape
• Saddle joints
– Each articular surface has concave and
convex surfaces
– Classified as biaxial joints
Synovial Joints Classified
by Shape
Synovial Joints Classified
by Shape
• Ball-and-socket joints
– Spherical head of one bone fits into round
socket of another
– Classified as multiaxial – allow
movement in all axes
– Examples: shoulder and hip joints
Ball-and-Socket Joint
Selected Synovial Joints
• Temporomandibular joint (TMJ)
– Lies anterior to the ear
– Head of the mandible articulates with the
mandibular fossa
– Two surfaces of the articular disc allow two
kinds of movement
• Hinge-like movement
• Superior surface of disc glides anteriorly
The Temporomandibular
Joint
Selected Synovial Joints
• Shoulder (Glenohumeral) joint
– The most freely movable joint – lacks
stability
– Articular capsule is thin and loose
– Muscle tendons contribute to joint stability
Glenohumeral Joint
Selected Synovial Joints
• Elbow joint
– Allows flexion and extension
– The humerus' articulation with ulna forms
the hinge
– Tendons of biceps and triceps brachii
provide stability
Elbow Joint
Elbow Joint
Selected Synovial Joints
• Hip joint
– A ball-and-socket structure
– Movements occur in all axes – limited by
ligaments and acetabulum
– Head of femur articulates with acetabulum
– Muscle tendons contribute somewhat to
stability
– Stability comes chiefly from acetabulum
and capsular ligaments
Frontal Section and
Anterior View of the Hip
Joint
Posterior View of the Hip
Joint
Selected Synovial Joints
• Knee joint
– The largest and most complex joint
– Primarily acts as a hinge joint
– Has some capacity for rotation when leg is
flexed
– Structurally considered compound and
bicondyloid
– Two fibrocartilage menisci occur within the
joint cavity
Sagittal Section and
Superior View of Knee
Joint
Sagittal Section and
Superior View of Knee
Joint
Knee Joint
• Capsule of knee joint
– Covers posterior and lateral aspects of the
knee
– Covers tibial and femoral condyles
– Does not cover the anterior aspect of the
knee
• Anteriorly – covered by three ligaments
– Patellar, medial, and lateral retinacula
Anterior View of Knee
Knee Joint
• Ligaments of the knee joint
– Become taut when knee is extended
– These extracapsular ligaments are
• Fibular and tibial collateral ligament
• Oblique popliteal ligament
• Arcuate popliteal ligament
Posterior View of Knee
Joint
Knee Joint
• Intracapsular ligaments
– Cruciate ligaments – cross each other like
an “X”
– Each runs from the proximal tibia to the
distal femur
• Anterior cruciate ligament
• Posterior cruciate ligament
Anterior View of Flexed
Knee
Knee Joint
• Cruciate ligaments
– Prevent undesirable movements at the
knee joint
Selected Synovial Joint
• Ankle Joint
– A hinge joint between:
• United inferior ends of tibia and fibula
• And the talus of the foot
• Allows dorsiflexion and plantar flexion
only
Ligaments of the Ankle
Joint
Ligaments of the Ankle
Joint
Ligaments of the Ankle
Joint
Disorders of Joints
• Structure of joints makes them prone to
traumatic stress
• Function of joints makes them subject
to friction and wear
• Affected by inflammatory and
degenerative processes
Joint Injuries
• Sprains – ligaments of a reinforcing
joint are stretched or torn
• Dislocation – occurs when the bones of
a joint are forced out of alignment
• Torn cartilage – common injury to
meniscus of knee joint
Inflammatory and
Degenerative Conditions
• Bursitis – inflammation of a bursa do to
injury or friction
• Tendonitis – inflammation of a tendon
sheath
Inflammatory and
Degenerative Conditions
• Arthritis – describes over 100 kinds of
joint-damaging diseases
– Osteoarthritis – most common type –
“wear and tear” arthritis
– Rheumatoid arthritis – a chronic
inflammatory disorder
– Gouty arthritis (gout) – uric acid build-up
causes pain in joints
• Lyme disease – inflammatory disease
often resulting in joint pain
The Joints Throughout Life
• Synovial joints develop from
mesenchyme
• By week 8 of fetal development, joints
resemble adult joints
– Outer region of mesenchyme becomes
fibrous joint capsule
– Inner region becomes the joint cavity